Catheter-based optical systems are applicable to a number of diagnostic and therapeutic medical applications. Optical coherence tomography is used to provide spatial resolution, enabling the imaging of internal structures. Spectroscopy is used to characterize the composition of structures, enabling the diagnosis of medical conditions, by differentiating between cancerous, dysplastic, and normal tissue structures. Ablation systems are used to remove or destroy structures within the body to address various diseases, such as tachycardias, tumors, and coronary artery disease, for example.
For example, in one specific spectroscopic application, a tunable laser source is used to scan a spectral band of interest, such as a scan band in the near infrared or 850 nanometers (nm) to 1–2 micrometers (μm), for example. The generated light is used to illuminate tissue in a target area in vivo using the catheter. Diffusely reflected light resulting from the illumination is then collected and transmitted to a detector and a spectral response resolved. The response is used to assess the state of the tissue.
One specific example is the diagnosis of atherosclerosis, and the identification of atherosclerotic lesions or plaques. This is an arterial disorder involving the intimae of medium- or large-sized arteries, including the aortic, carotid, coronary, and cerebral arteries. Efforts are being made to spectroscopically analyze blood vessel walls and characterize any atherosclerotic lesions.
These catheter-based optical systems typically comprise a console, such as hand-held, rack mountable, or floor unit. A fiber optical probe or catheter connects to the console. The catheter is used to deliver optical energy to and/or receive energy from regions of interest on or in the patient.
The catheter is usually plugged into an optical port of the console. Many times the catheter is disposable, being limited to one time usage. Therefore, after usage, it must be disconnected and disposed of. Even if the catheter is not disposable, it must be disconnected for sterilization between usages.
The quality of the optical connection between the console and the catheter is relevant to the optical performance of the machine. A damaged or dirty interface minimally can degrade the power of the optical signal transmitted to the patient and/or received from the patient. In spectroscopic applications, for example, a dirty interface can also lead to spurious results.
One method for assessing the quality of the optical interface is to additionally provide the console with a calibration port. The end of the probe is inserted into the calibration port and the optical system energized. This allows the optical system to be tested at the point of delivery.